Ophthalmic lenses have already been proposed, which are comprised of a base lens and a film which is laminated on an optical surface of the base lens. The film has two parallel external surfaces. Then the optical dioptre function of the ophthalmic lens depends on the shape of the surface of the base lens which supports the film. As a consequence, any change in the shape of the base lens surface with respect to a target surface results in optical defects such as image distortions or optical aberrations. Such distortions and aberrations are most significant in a center zone of the lens, and may lead to discarding the final product. Production yield is then reduced.
But the production method of the final ophthalmic lens generally includes one or several heating steps. Such heating step may be necessary for implementing adhesive means for retaining the film on base lens, or for providing the resulting ophthalmic lens with an additional hardcoating or functionalizing coating. Due to stresses internal to the film, the film may vary in shape during the heating step, and because it is adhered to the lens base, the surface of this latter may be altered. Thus image distortions and/or optical aberrations may appear for the ophthalmic lens. The internal stresses of the film may have various causes, including its own production method and a preforming step for providing the film with curvature when the film-receiving surface of the base lens is curved. Then it is known, in particular from the international patent application PCT/US2009/067820, to perform a first heating of the film before it is assembled with the base lens, up to a maximum pre-assembling temperature which is higher than the maximum temperature of a post-assembling heating step which is performed after the film structure has been connected to the base lens. Such pre-assembling heating of the film reduces its internal stresses, so that the base lens is less altered in curvature values during the post-assembling heating step.
However, the pre-assembling heating step may still cause image distortions or optical aberrations for the final ophthalmic lens. Indeed, the maximum temperature of the post-assembling heating step may be high, depending on the function of this post-assembling heating. In particular, hardcoating and/or some of the functionalizing coatings used require post-assembling heating temperatures which are higher than the glass-transition temperature of the base lens. Because this glass-transition temperature is exceeded, the base lens is changed in shape and curvature values, thus causing image distortions and optical aberrations again.
Therefore, an object of the present invention is to provide ophthalmic lenses each comprised of a base lens and a film structure, which are less altered in shape and curvature values during a post-assembling heating step with maximum temperature higher than the glass-transition temperature of the base lens.
Another object of the invention is to provide such ophthalmic lens devoid of image distortion and optical aberration, although it is heated above the glass-transition temperature of the corresponding base lens after the film has been assembled with the base lens.
Still another object of the invention is to manufacture such ophthalmic lenses with improved production yield while meeting the quality requirements of the ophthalmic applications.